The present invention broadly relates to a wet press and, more specifically, pertains to a new and improved construction of a wet press for dewatering a web of material.
Generally speaking, the wet press of the present invention comprises a rotating roll and a contact pressure device between which the web of material is guided in a press nip together with at least one water-absorbent belt along a portion of the circumference of the rotating roll. The contact pressure device comprises at least two contact pressure elements sequentially arranged in the direction of travel of the web of material which exert a pressing force which increases in such direction of travel of the web of material.
In other words, the wet press for dewatering a web of material comprises a rotating roll having a circumference, a contact pressure device and at least one water-absorbent belt. The contact pressure device and the rotating roll define a press nip therebetween. The web of material is guided conjointly with the water-absorbent belt between the contact pressure device and the rotating roll through the press nip and along a portion of the circumference of the rotating roll. The web of material has a predetermined direction of travel. The contact pressure device comprises at least two contact pressure elements arranged sequentially in the direction of web travel for exerting a contact pressure which increases in such direction of web travel.
Such wet presses are described, for instance, in the U.S. Pat. No. 3,783,097, granted Jan. 1, 1974 or the German Pat. No. 3,105,276 and serve for dewatering, for instance, a web of paper or pulp or another fibrous material. The web of material is guided through a press nip together with, for instance, a water-absorbent felt belt and a water-impervious pressure belt. The press nip is formed by a roll and several contact pressure elements arranged sequentially in the direction of travel of the web of material. In order to achieve a good dewatering effect, the pressing force of the sequentially arranged contact pressure elements increases in the direction of web travel up to a maximum value and then is reduced to zero as suddenly as possible in order to avoid a re-moistening.
The contact pressure elements can be constructed as pressure ledges or beams extending over the entire width of the web of material. As the roll deflects in operation there is no guarantee that the contact pressure devices will exert the same pressure over the entire width of the web of material. It can also be desirable to vary the pressure exerted on the web of material over the width of the web of material. With contact pressure elements constructed as ledges which are continuous over the entire web width, this is, however, difficult. In order to be able to regulate a contact pressure or pressing force uniformly over the roll width or to regulate a desired pressure profile, the contact pressure elements must be divided into a number of individual pressure or support elements arranged adjacent to one another in a row transverse to the direction of travel of the web of material. Even if the individual pressure or support elements are arranged in intimate contact over the roll width, a pressure gradient necessarily arises at the border between two adjacent pressure elements which leads to a non-uniform dewatering over the width of the web of material and, for instance, can result in stripes in the fabricated paper which are intolerable or hardly tolerable in practice.